典型草地土壤好氧甲烷氧化的微生物生态过程

Aerobic methane oxidation in typical grassland soil

摘要:

[目的]针对我国甘肃三个典型生态区草地土壤（玛曲MQ、临泽LZ和环县HX），研究其甲烷氧化潜力、甲烷氧化菌（methane-oxidizing bacteria，MOB）丰度及可能存在的群落分异规律。[方法]通过原位分析、室内高浓度甲烷模拟培养三种典型土壤及实时荧光定量、高通量测序的方法研究甲烷氧化菌标靶基因pmoA序列的组成及其丰度变化规律。[结果]三种典型草地土壤的原位甲烷氧化菌的丰度存在显著差异，表现为MQ > HX > LZ，其数量范围为为0.18-6.86×10⁷g/d.w.s.；甲烷氧化潜力也表现出类似规律，其通量为109-169 mg/（m²·h）；甲烷氧化潜力与原位土壤中甲烷氧化菌丰度有正相关。三种草地土壤甲烷氧化菌存在明显的空间异质性，采用高通量测序的方法，发现三种草地原位土壤中的优势类群为USCγ（Upland Soil Cluster gamma，USCγ）；然而，室内高浓度甲烷氧化过程中，传统的甲烷氧化菌均发生明显增加，MQ土壤中TypeⅡ的Methylocystis为优势类群，而LZ和HX土壤的优势类群均为TypeⅠ型Methylosarcina。[结论]这些研究结果表明，我国甘肃典型草地土壤中也存在难培养的大气甲烷氧化菌和经典的可培养甲烷氧化菌，这些微生物极可能氧化极低浓度的大气甲烷，也可能利用闭蓄于土壤中的高浓度甲烷生长。未来应采用先进技术原位观测大气甲烷氧化过程并分离相应微生物类群，研究草地土壤甲烷氧化菌地理分异规律及其环境驱动机制。

Abstract:

[Objective] The soil methane uptake potential, abundance and community structure of methane-oxidizing bacteria were investigated in three grasslands located in three different ecoregions:Maqu, Linze and Huanxian of Gansu province of China. [Methods] Eight days incubation of soil with elevated concentration of methane was carried out to measure methane uptake capacity. The methane-oxidizing bacteria abundance was quantified by real time quantitive PCR targeting particulate methane monooxygenase coding gene (pmoA) in soils. The methane-oxidizing bacteria community structure was assessed by amplicon MiSeq sequencing. [Results] The potential of methane oxidation of three grassland soils ranged from 108.53±13.12 to 168.87±18.57 mg/(m²·h). The abundance of methane-oxidizing bacteria ranged from 1.76×10⁷ to 6.86×10⁷ pmoA gene copies g/d.w.s. The methane oxidation potential was positively correlated with methane-oxidizing bacteria abundance at day 0 (R²=0.5537). MiSeq sequencing analysis revealed significant spatial heterogeneity of methane-oxidizing bacteria community within the same grassland type. The Upland Soil Cluster gamma belonging to uncultured atmospheric methane oxidizers was the dominant methanotrophic lineage within methane-oxidizing bacteria gene types found in situ grassland soils. However, the conventional methane-oxidizing bacteria increased significantly after incubated these soils under high concentration methane, such as Methylocystis in Maqu soil and Methylosarcina in Linze and Huanxian soils. [Conclusion] Both uncultured atmospheric methane-oxidizing bacteria and the conventional methane-oxidizing bacteria may play an important role in the process of methane oxidation in the typical grassland soils in Gansu province of China. These microbes are very likely to oxidize the trace methane in atmosphere, and may also grow with high concentration of methane that stored in the soil. In the future, advanced techniques should be used to observe the atmospheric methane oxidation process in situ and to isolate the corresponding microbial groups, and finally reveal the geographical differentiation of methane-oxidizing bacteria in grassland soils and the environmental driving mechanism.